A block pressed against the vertical wall is in equilibrium. The minimum coefficient of  friction is:-

A body of weight $50 \,N$ placed on a horizontal surface is just moved by a force of $28.2\, N$. The frictional force and the normal reaction are

What is the maximum value of the force $F$ such that the block shown in the arrangement, does not move ........ $N$

A lift is moving downwards with an acceleration equal to acceleration due to gravity. $A$ body of mass $M$ kept on the floor of the lift is pulled horizontally. If the coefficient of friction is $\mu $, if the lift is moving upwards with a uniform velocity, then the frictional resistance offered by the body is

A pen of mass $m$ is lying on a piece of paper of mass $M$ placed on a rough table. If the coefficients of friction between the pen and paper and the paper and the table are $\mu_1$ and $\mu_2$, respectively. Then, the minimum horizontal force with which the paper has to be pulled for the pen to start slipping is given by

The limiting value of static friction between two contact surfaces is ...........